1. Field of the Invention
This invention relates to a method of and apparatus for reading out a radiation image, and more particularly to a method of and apparatus for reading out a radiation image where an image read-out means is moved back and forth relatively to a stimulable phosphor sheet.
2. Description of the Related Art
When certain kinds of phosphor are exposed to a radiation such as X-rays, xcex1-rays, xcex2-rays, xcex3-rays, electron beams, ultraviolet rays and the like, they store a part of energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating light such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is generally referred to as xe2x80x9ca stimulable phosphorxe2x80x9d. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as xe2x80x9cstimulated emissionxe2x80x9d. There has been known a radiation image recording and reproducing system in which a stimulable phosphor sheet (a sheet provided with a layer of the stimulable phosphor) is exposed to a radiation passing through an object such as a human body to have a radiation image of the object stored on the stimulable phosphor sheet as a latent image, stimulating light such as a laser beam is projected onto the stimulable phosphor sheet, and the stimulated emission emitted from the stimulable phosphor sheet is photoelectrically detected, thereby obtaining an image signal (a radiation image signal) representing a radiation image of the object. See, for instance, Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)-11395 and 56(1981)-11397.
This system is advantageous over the conventional radiograph system using silver halide photographic film in that a radiation image can be recorded over a much wider range of exposure to a radiation. That is, it has been found that the amount of radiation energy stored in the stimulable phosphor sheet as a latent radiation image and the amount of stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light are proportional to each other over a very wide range. Accordingly, even if the exposure of the stimulable phosphor sheet to the radiation is greatly increased or reduced under various image taking conditions, an image recorded on the stimulable phosphor sheet can be accurately reproduced by accurately converting the amount of stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light to an electric image signal.
In apparatuses for reading out an image from the stimulable phosphor sheet (apparatuses for projecting stimulating light and photoelectrically detecting the stimulated emission, the image read-out means comprising a stimulating light projecting means for projecting stimulating light onto a stimulable phosphor sheet on which a radiation image has been recorded and a photoelectric convertor means which photoelectrically converts the stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light to an electric signal is moved back and forth relatively to the stimulable phosphor sheet and the radiation image is read out generally only during the forward movement of the photoelectric convertor means relatively to the stimulable phosphor sheet.
Further, a radiation image recorded on the stimulable phosphor sheet can be erased by exposing the stimulable phosphor sheet to erasing light and the erased stimulable phosphor sheet can be reused to record and reproducing a radiation image. The residual radiation image still held by a stimulable phosphor sheet after an image is read out from the stimulable phosphor sheet by projecting stimulating light onto the stimulable phosphor sheet is generally erased by projecting a predetermined amount of erasing light onto the stimulable phosphor sheet sufficient to release radiation energy still held by the stimulable phosphor sheet as a latent radiation image to such an extent that the stimulable phosphor sheet becomes reusable irrespective of the magnitude of the residual radiation energy.
However, when the radiation image is read out only during the forward movement of the photoelectric convertor means relatively to the stimulable phosphor sheet, the time required for the photoelectric convertor means to return to the original position from the end of the forward movement thereof becomes a dead time during which no operation useful to obtain a radiation image is performed, which elongates the cycle time for reading out radiation images from the stimulable phosphor sheets and deteriorates the working efficiency of the radiation image read-out apparatus.
Further projecting the erasing light onto the stimulable phosphor sheet in an amount sufficient to release the residual radiation energy can lead to waste of power. That is, the erasing light can be projected onto the stimulable phosphor sheet in an amount more than necessary to release the residual radiation energy when the residual radiation energy is relatively small. Further, projecting the erasing light in an amount more than necessary shortens the service life of the erasing light source.
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and apparatus for reading out a radiation image which can improve the working efficiency in reading out a radiation image from a stimulable phosphor sheet.
Another object of the present invention is to provided a method of and apparatus for reading out a radiation image which can improve the energy efficiency in erasing a stimulable phosphor sheet by projecting erasing light onto the stimulable phosphor sheet.
In accordance with the present invention, a stimulable phosphor sheet bearing thereon a radiation image is moved back and forth in first and second directions opposite to each other relatively to an image read-out means in order to two-dimensionally expose the stimulable phosphor sheet to stimulating light, and stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is detected during both the forward movement (movement in the first direction) and the backward movement (movement in the direction) of the stimulable phosphor sheet to obtain first and second image signals on the basis of the stimulated emission detected during the respective movements of the stimulable phosphor sheet, and the second image signal is used in various ways, thereby effectively using the backward movement of the stimulable phosphor sheet relatively to the image read-out means.
That is, in accordance with a first aspect of the present invention, there is provided a radiation image read-out method in which stimulating light is projected onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line by an image read-out means while one of the stimulable phosphor sheet and the image read-out means is being moved in a sub-scanning direction intersecting the main scanning direction relatively to the other and stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is detected by the image read-out means and is photoelectrically converted to an electric image signal thereby, wherein the improvement comprises the steps of
moving back and forth one of the stimulable phosphor sheet and the image read-out means in the sub-scanning direction relatively to the other,
detecting stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during both the forward movement and the backward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain first and second image signals on the basis of the stimulated emission detected during the respective movements of said one of the stimulable phosphor sheet and the image read-out means, and
obtaining an image signal representing the radiation image on the stimulable phosphor sheet on the basis of the first and second image signals.
In accordance with a second aspect of the present invention, there is provided a radiation image read-out method in which stimulating light is projected onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line by an image read-out means while one of the stimulable phosphor sheet and the image read-out means is being moved in a sub-scanning direction intersecting the main scanning direction relatively to the other and stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is detected by the image read-out means and is photoelectrically converted to an electric image signal thereby, wherein the improvement comprises the steps of
moving the image read-out means back and forth in the sub-scanning direction relatively to the stimulable phosphor sheet,
detecting stimulated emission emitted from a first stimulable phosphor sheet upon exposure to the stimulating light during the forward movement of the image read-out means to obtain a first image signal representing a first radiation image recorded on the first stimulable phosphor sheet on the basis of the stimulated emission detected during the forward movement of the image read-out means relatively to the stimulable phosphor sheet,
detecting stimulated emission emitted from a second stimulable phosphor sheet upon exposure to the stimulating light during the backward movement of the image read-out means to obtain a second image signal representing a second radiation image recorded on the second stimulable phosphor sheet on the basis of the stimulated emission detected during the backward movement of the image read-out means relatively to the stimulable phosphor sheet.
In accordance with a third aspect of the present invention, there is provided a radiation image read-out method in which stimulating light is projected onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line by an image read-out means while one of the stimulable phosphor sheet and the image read-out means is being moved in a sub-scanning direction intersecting the main scanning direction relatively to the other and stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is detected by the image read-out means and is photoelectrically converted to an electric image signal thereby, wherein the improvement comprises the steps of
moving back and forth one of the stimulable phosphor sheet and the image read-out means in the sub-scanning direction relatively to the other,
detecting stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during the forward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain a first image signal representing the radiation image on the basis of the stimulated emission detected during the forward movement of said one of the stimulable phosphor sheet and the image read-out means,
detecting stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during the backward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain a second image signal representing the residual radiation image on the basis of the stimulated emission detected during the backward movement of said one of the stimulable phosphor sheet and the image read-out means, and
obtaining information useful to determine the level of erasing light on the basis of the second image signal.
The image read-out means comprises a stimulating light projecting means which projects stimulating light onto a stimulable phosphor sheet along a main scanning line and an image signal generating means which generates an image signal representing a radiation image on the stimulable phosphor sheet by photoelectric conversion of stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light.
In accordance with a fourth aspect of the present invention, there is provided a radiation image read-out apparatus comprising an image read-out means provided with a stimulating light projecting means which projects stimulating light onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line, and a photoelectric convertor means which detects stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light, and a sub-scanning means which moves one of the stimulable phosphor sheet and the image read-out means in a sub-scanning direction intersecting the main scanning direction relatively to the other, the image read-out means causing the photoelectric convertor means to detect stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light while one of the stimulable phosphor sheet and the image read-out means is moved in the sub-scanning direction relatively to the other and to photoelectrically convert the stimulated emission to an electric signal, thereby obtaining an electric image signal representing the radiation image on the stimulable phosphor sheet, wherein the improvement comprises that
the sub-scanning means moves back and forth one of the stimulable phosphor sheet and the image read-out means in the sub-scanning direction relatively to the other, and
the image read-out means detects stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during both the forward movement and the backward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain first and second image signals on the basis of the stimulated emission detected during the respective movements of said one of the stimulable phosphor sheet and the image read-out means, and obtains an image signal representing the radiation image on the stimulable phosphor sheet on the basis of the first and second image signals.
The photoelectric convertor means may comprise a CCD.
In accordance with a fifth aspect of the present invention, there is provided a radiation image read-out apparatus comprising an image read-out means provided with a stimulating light projecting means which projects stimulating light onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line, and a photoelectric convertor means which detects stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light, and a sub-scanning means which moves the image read-out means in a sub-scanning direction intersecting the main scanning direction relatively to the stimulable phosphor sheet, the image read-out means causing the photoelectric convertor means to detect stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light while the stimulable phosphor sheet is moved in the sub-scanning direction relatively to the stimulable phosphor sheet and to photoelectrically convert the stimulated emission to an electric signal, thereby obtaining an electric image signal representing the radiation image on the stimulable phosphor sheet, wherein the improvement comprises that
the sub-scanning means moves the image read-out means back and forth in the sub-scanning direction relatively to the stimulable phosphor sheet, and
the image read-out means detects stimulated emission emitted from a first stimulable phosphor sheet upon exposure to the stimulating light during the forward movement of the image read-out means to obtain a first image signal representing a first radiation image recorded on the stimulable phosphor sheet on the basis of the stimulated emission detected during the forward movement of the image read-out means relatively to the stimulable phosphor sheet, and detects stimulated emission emitted from a second stimulable phosphor sheet upon exposure to the stimulating light during the backward movement of the image read-out means to obtain a second image signal representing a second radiation image recorded on the second stimulable phosphor sheet on the basis of the stimulated emission detected during the backward movement of the image read-out means relatively to the stimulable phosphor sheet.
In accordance with a sixth aspect of the present invention, there is provided a radiation image read-out apparatus comprising an image read-out means provided with a stimulating light projecting means which projects stimulating light onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line, and a photoelectric convertor means which detects stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light, and a sub-scanning means which moves one of the stimulable phosphor sheet and the image read-out means in a sub-scanning direction intersecting the main scanning direction relatively to the other, the image read-out means causing the photoelectric convertor means to detect stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light while one of the stimulable phosphor sheet and the image read-out means is moved in the sub-scanning direction relatively to the other and to photoelectrically convert the stimulated emission to an electric signal, thereby obtaining an electric image signal representing the radiation image on the stimulable phosphor sheet, wherein the improvement comprises that
the sub-scanning means moves back and forth one of the stimulable phosphor sheet and the image read-out means in the sub-scanning direction relatively to the other, and
the image read-out means detects stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during the forward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain a first image signal representing the radiation image on the basis of the stimulated emission detected during the forward movement of said one of the stimulable phosphor sheet and the image read-out means, and detects stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during the backward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain a second image signal representing the residual radiation image on the basis of the stimulated emission detected during the backward movement of said one of the stimulable phosphor sheet and the image read-out means, thereby obtaining information useful to determine the level of erasing light on the basis of the second image signal.
The expression xe2x80x9cmove one of the stimulable phosphor sheet and the image read-out means relatively to the otherxe2x80x9d means that the stimulable phosphor sheet is moved relatively to the image read-out means, that the image read-out means is moved relatively to the stimulable phosphor sheet, or that both the stimulable phosphor sheet and the image read-out means are moved relatively to the other. At this time, when the image read-out means is moved, only the part thereof necessary to obtain the image signal may be moved.
The xe2x80x9cinformation useful to determine the level of erasing lightxe2x80x9d may be, for instance, information representing the amount of erasing light necessary to erase the residual radiation image.
In the method in accordance with the second aspect of the present invention and the apparatus in accordance with the fifth aspect of the present invention, the first and second stimulable phosphor sheets may be either the same or different from each other. That is, the first and second radiation images may be recorded on a stimulable phosphor sheet so that the second radiation is recorded on the stimulable phosphor sheet after the first radiation image is read out during the forward movement of the image read-out means and is read out during the backward movement of the image read-out means, or may be recorded on respective stimulable phosphor sheets so that, for instance, the first stimulable phosphor sheet is replaced with the second stimulable phosphor sheet after the forward movement of the image read-out means and the image read-out means reads out the first radiation image from the first stimulable phosphor sheet during the forward movement of the image read-out means and reads out the second radiation image from the second stimulable phosphor sheet during the backward movement of the image read-out means.
In the method in accordance with the first aspect of the present invention and the apparatus in accordance with the fourth aspect of the present invention, the image signal representing a radiation image recorded on the stimulable phosphor sheet is read out during both the forward movement and the backward movement of the stimulable phosphor sheet and/or the image read-out means, and accordingly, the backward movement can be well utilized, whereby the overall working efficiency can be improved.
When the photoelectric convertor means comprises a CCD, which is narrower in allowable input range than a photomultiplier (about {fraction (1/10)}), and the amount of stimulated emission emitted from particular areas of the stimulable phosphor sheet in the forward movement overflows the allowable input range of the CCD, the amount of stimulated emission emitted from the stimulable phosphor sheet in the backward movement cannot overflow the allowable input range of the CCD or overflows at less areas than in the forward movement since radiation energy stored in the stimulable phosphor sheet has been once released in the forward movement, and accordingly, the image signal components for the particular areas where the stimulated emission overflows the allowable input range of the CCD can be filled with the image signal components obtained in the backward movement. Thus, a more precise image signal can be obtained when an image signal representing a radiation image is generated on the basis of both the image signals respectively obtained during the forward movement and the backward movement.
In the method in accordance with the second aspect of the present invention and the apparatus in accordance with the fifth aspect of the present invention, two radiation images can be read out during one reciprocation of the image read-out means, and accordingly, the working efficiency can be improved as compared with the conventional method and apparatus where a radiation image is read out during only the forward movement.
In the method in accordance with the third aspect of the present invention and the apparatus in accordance with the sixth aspect of the present invention, by determining the amount of erasing light to be projected onto the stimulable phosphor sheet on the basis of the information obtained during the backward movement, the erasing light can be prevented from being projected onto the stimulable phosphor sheet in an amount more than necessary to release the residual radiation energy and the erasing light source can be prevented from being shortened in its service life.